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391.
A. G. Yahnin I. V. Despirak A. A. Lubchich B. V. Kozelov N. P. Dmitrieva M. A. Shukhtina H. K Biernat 《Space Science Reviews》2006,122(1-4):97-106
Although the auroral substorm has been long regarded as a manifestation of the magnetospheric substorm, a direct relation
of active auroras to certain magnetospheric processes is still debatable. To investigate the relationship, we combine the
data of the UV imager onboard the Polar satellite with plasma and magnetic field measurements by the Geotail spacecraft. The
poleward edge of the auroral bulge, as determined from the images obtained at the LHBL passband, is found to be conjugated
with the region where the oppositely directed fast plasma flows observed in the near-Earth plasma sheet during substorms are
generated. We conclude that the auroras forming the bulge are due to the near-Earth reconnection process. This implies that
the magnetic flux through the auroral bulge is equal to the flux dissipated in the magnetotail during the substorm. Comparison
of the magnetic flux through the auroral bulge with the magnetic flux accumulated in the tail lobe during the growth phase
shows that these parameters have the comparable values. This is a clear evidence of the loading–unloading scheme of substorm
development. It is shown that the area of the auroral bulge developing during substorm is proportional to the total (magnetic
plus plasma) pressure decrease in the magnetotail. These findings stress the importance of auroral bulge observations for
monitoring of substorm intensity in terms of the magnetic flux and energy dissipation. 相似文献
392.
Y. Futaana S. Barabash A. Grigoriev D. Winningham R. Frahm M. Yamauchi R. Lundin 《Space Science Reviews》2006,126(1-4):315-332
As a part of the global plasma environment study of Mars and its response to the solar wind, we have analyzed a peculiar case
of the subsolar energetic neutral atom (ENA) jet observed on June 7, 2004 by the Neutral Particle Detector (NPD) on board
the Mars Express satellite. The “subsolar ENA jet” is generated by the interaction between the solar wind and the Martian
exosphere, and is one of the most intense sources of ENA flux observed in the vicinity of Mars. On June 7, 2004 (orbit 485
of Mars Express), the NPD observed a very intense subsolar ENA jet, which then abruptly decreased within ∼10 sec followed
by quasi-periodic (∼1 min) flux variations. Simultaneously, the plasma sensors detected a solar wind structure, which was
most likely an interplanetary shock surface. The abrupt decrease of the ENA flux and the quasi-periodic flux variations can
be understood in the framework of the global response of the Martian plasma obstacle to the interplanetary shock. The generation
region of the subsolar ENA jet was pushed towards the planet by the interplanetary shock; and therefore, Mars Express went
out of the ENA jet region. Associated global vibrations of the Martian plasma obstacle may have been the cause of the quasi-periodic
flux variations of the ENA flux at the spacecraft location. 相似文献
393.
We present a brief introduction to the essential physics of coronal mass ejections as well as a review of theory and models
of CME initiation, solar energetic particle (SEP) acceleration, and shock propagation. A brief review of the history of CME
models demonstrates steady progress toward an understanding of CME initiation, but it is clear that the question of what initiates
CMEs has still not been solved. For illustration, we focus on the flux cancellation model and the breakout model. We contrast
the similarities and differences between these models, and we examine how their essential features compare with observations.
We review the generation of shocks by CMEs. We also outline the theoretical ideas behind the origin of a gradual SEP event
at the evolving CME-driven coronal/interplanetary shock and the origin of “impulsive” SEP events at flare sites of magnetic
reconnection below CMEs. We argue that future developments in models require focused study of “campaign events” to best utilize
the wealth of available CME and SEP observations. 相似文献
394.
Structure of a two-phase flow of boiling water at low-head adiabatic efflux through the laval nozzle
The critical flow conditions and structural forms of a two-phase flow that is formed during water efflux from the region of moderate and low pressures into a rarefied medium are analyzed. The difference in the structural forms of a flow realized at the low-head efflux from the structure of a flow occurring in the fluid flow with moderate and high initial pressures is established. The critical pressure differential characterizing the establishment of the maximum flowrate is determined and the decisive influence of turbulence on the vapor phase generation and flow conditions of a two-phase medium is shown. 相似文献
395.
D. B. Reisenfeld D. S. Burnett R. H. Becker A. G. Grimberg V. S. Heber C. M. Hohenberg A. J. G. Jurewicz A. Meshik R. O. Pepin J. M. Raines D. J. Schlutter R. Wieler R. C. Wiens T. H. Zurbuchen 《Space Science Reviews》2007,130(1-4):79-86
Analysis of the Genesis samples is underway. Preliminary elemental abundances based on Genesis sample analyses are in good
agreement with in situ-measured elemental abundances made by ACE/SWICS during the Genesis collection period. Comparison of
these abundances with those of earlier solar cycles indicates that the solar wind composition is relatively stable between
cycles for a given type of flow. ACE/SWICS measurements for the Genesis collection period also show a continuum in compositional
variation as a function of velocity for the quasi-stationary flow that defies the simple binning of samples into their sources
of coronal hole (CH) and interstream (IS). 相似文献
396.
MESSENGER: Exploring Mercury’s Magnetosphere 总被引:1,自引:0,他引:1
James A. Slavin Stamatios M. Krimigis Mario H. Acuña Brian J. Anderson Daniel N. Baker Patrick L. Koehn Haje Korth Stefano Livi Barry H. Mauk Sean C. Solomon Thomas H. Zurbuchen 《Space Science Reviews》2007,131(1-4):133-160
The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission to Mercury offers our first opportunity
to explore this planet’s miniature magnetosphere since the brief flybys of Mariner 10. Mercury’s magnetosphere is unique in
many respects. The magnetosphere of Mercury is among the smallest in the solar system; its magnetic field typically stands
off the solar wind only ∼1000 to 2000 km above the surface. For this reason there are no closed drift paths for energetic
particles and, hence, no radiation belts. Magnetic reconnection at the dayside magnetopause may erode the subsolar magnetosphere,
allowing solar wind ions to impact directly the regolith. Inductive currents in Mercury’s interior may act to modify the solar
wind interaction by resisting changes due to solar wind pressure variations. Indeed, observations of these induction effects
may be an important source of information on the state of Mercury’s interior. In addition, Mercury’s magnetosphere is the
only one with its defining magnetic flux tubes rooted beneath the solid surface as opposed to an atmosphere with a conductive
ionospheric layer. This lack of an ionosphere is probably the underlying reason for the brevity of the very intense, but short-lived,
∼1–2 min, substorm-like energetic particle events observed by Mariner 10 during its first traversal of Mercury’s magnetic
tail. Because of Mercury’s proximity to the sun, 0.3–0.5 AU, this magnetosphere experiences the most extreme driving forces
in the solar system. All of these factors are expected to produce complicated interactions involving the exchange and recycling
of neutrals and ions among the solar wind, magnetosphere, and regolith. The electrodynamics of Mercury’s magnetosphere are
expected to be equally complex, with strong forcing by the solar wind, magnetic reconnection, and pick-up of planetary ions
all playing roles in the generation of field-aligned electric currents. However, these field-aligned currents do not close
in an ionosphere, but in some other manner. In addition to the insights into magnetospheric physics offered by study of the
solar wind–Mercury system, quantitative specification of the “external” magnetic field generated by magnetospheric currents
is necessary for accurate determination of the strength and multi-polar decomposition of Mercury’s intrinsic magnetic field.
MESSENGER’s highly capable instrumentation and broad orbital coverage will greatly advance our understanding of both the origin
of Mercury’s magnetic field and the acceleration of charged particles in small magnetospheres. In this article, we review
what is known about Mercury’s magnetosphere and describe the MESSENGER science team’s strategy for obtaining answers to the
outstanding science questions surrounding the interaction of the solar wind with Mercury and its small, but dynamic, magnetosphere. 相似文献
397.
L. Colangeli J. J. Lopez-Moreno P. Palumbo J. Rodriguez M. Cosi V. Della Corte F. Esposito M. Fulle M. Herranz J. M. Jeronimo A. Lopez-Jimenez E. Mazzotta Epifani R. Morales F. Moreno E. Palomba A. Rotundi 《Space Science Reviews》2007,128(1-4):803-821
The Grain Impact Analyser and Dust Accumulator (GIADA) onboard the ROSETTA mission to comet 67P/Churyumov–Gerasimenko is devoted
to study the cometary dust environment. Thanks to the rendezvous configuration of the mission, GIADA will be plunged in the
dust environment of the coma and will be able to explore dust flux evolution and grain dynamic properties with position and
time. This will represent a unique opportunity to perform measurements on key parameters that no ground-based observation
or fly-by mission is able to obtain and that no tail or coma model elaborated so far has been able to properly simulate. The
coma and nucleus properties shall be, then, clarified with consequent improvement of models describing inner and outer coma
evolution, but also of models about nucleus emission during different phases of its evolution. GIADA shall be capable to measure
mass/size of single particles larger than about 15 μm together with momentum in the range 6.5 × 10−10 ÷ 4.0 × 10−4 kg m s−1 for velocities up to about 300 m s−1. For micron/submicron particles the cumulative mass shall be detected with sensitivity 10−10 g. These performances are suitable to provide a statistically relevant set of data about dust physical and dynamic properties
in the dust environment expected for the target comet 67P/Churyumov–Gerasimenko. Pre-flight measurements and post-launch checkouts
demonstrate that GIADA is behaving as expected according to the design specifications.
The International GIADA Consortium (I, E, UK, F, D, USA). 相似文献
398.
R. C. Wiens D. S. Burnett C. M. Hohenberg A. Meshik V. Heber A. Grimberg R. Wieler D. B. Reisenfeld 《Space Science Reviews》2007,130(1-4):161-171
The Genesis mission returned samples of solar wind to Earth in September 2004 for ground-based analyses of solar-wind composition,
particularly for isotope ratios. Substrates, consisting mostly of high-purity semiconductor materials, were exposed to the
solar wind at L1 from December 2001 to April 2004. In addition to a bulk sample of the solar wind, separate samples of coronal
hole (CH), interstream (IS), and coronal mass ejection material were obtained. Although many substrates were broken upon landing
due to the failure to deploy the parachute, a number of results have been obtained, and most of the primary science objectives
will likely be met. These objectives include He, Ne, Ar, Kr, and Xe isotope ratios in the bulk solar wind and in different
solar-wind regimes, and 15N/14N and 18O/17O/16O to high precision. The greatest successes to date have been with the noble gases. Light noble gases from bulk solar wind
and separate solar-wind regime samples have now been analyzed. Helium results show clear evidence of isotopic fractionation
between CH and IS samples, consistent with simplistic Coulomb drag theory predictions of fractionation between the photosphere
and different solar-wind regimes, though fractionation by wave heating is also a possible explanation. Neon results from closed
system stepped etching of bulk metallic glass have revealed the nature of isotopic fractionation as a function of depth, which
in lunar samples have for years deceptively suggested the presence of an additional, energetic component in solar wind trapped
in lunar grains and meteorites. Isotope ratios of the heavy noble gases, nitrogen, and oxygen are in the process of being
measured. 相似文献
399.
R. Schwenn J. C. Raymond D. Alexander A. Ciaravella N. Gopalswamy R. Howard H. Hudson P. Kaufmann A. Klassen D. Maia G. Munoz-Martinez M. Pick M. Reiner N. Srivastava D. Tripathi A. Vourlidas Y.-M. Wang J. Zhang 《Space Science Reviews》2006,123(1-3):127-176
CMEs have been observed for over 30 years with a wide variety of instruments. It is now possible to derive detailed and quantitative information on CME morphology, velocity, acceleration and mass. Flares associated with CMEs are observed in X-rays, and several different radio signatures are also seen. Optical and UV spectra of CMEs both on the disk and at the limb provide velocities along the line of sight and diagnostics for temperature, density and composition. From the vast quantity of data we attempt to synthesize the current state of knowledge of the properties of CMEs, along with some specific observed characteristics that illuminate the physical processes occurring during CME eruption. These include the common three-part structures of CMEs, which is generally attributed to compressed material at the leading edge, a low-density magnetic bubble and dense prominence gas. Signatures of shock waves are seen, but the location of these shocks relative to the other structures and the occurrence rate at the heights where Solar Energetic Particles are produced remains controversial. The relationships among CMEs, Moreton waves, EIT waves, and EUV dimming are also cloudy. The close connection between CMEs and flares suggests that magnetic reconnection plays an important role in CME eruption and evolution. We discuss the evidence for reconnection in current sheets from white-light, X-ray, radio and UV observations. Finally, we summarize the requirements for future instrumentation that might answer the outstanding questions and the opportunities that new space-based and ground-based observatories will provide in the future. 相似文献
400.
A. Galli P. Wurz H. Lammer H. I. M. Lichtenegger R. Lundin S. Barabash A. Grigoriev M. Holmström H. Gunell 《Space Science Reviews》2006,126(1-4):447-467
We have evaluated the Lyman-α limb emission from the exospheric hydrogen of Mars measured by the neutral particle detector of the ASPERA-3 instrument on Mars Express in 2004 at low solar activity (solar activity index = 42, F10.7=100). We derive estimates for the hydrogen exobase density, n H = 1010 m?3, and for the apparent temperature, T > 600 K. We conclude that the limb emission measurement is dominated by a hydrogen component that is considerably hotter than the bulk temperature at the exobase. The derived values for the exosphere density and temperature are compared with similar measurements done by the Mariner space probes in the 1969. The values found with Mars Express and Mariner data are brought in a broader context of exosphere models including the possibility of having two hydrogen components in the Martian exosphere. The present observation of the Martian hydrogen exosphere is the first one at high altitudes during low solar activity, and shows that for low solar activity exospheric densities are not higher than for high solar activity. 相似文献